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Checkbox for mod inverse; calculations implemented

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This commit is contained in:
Barry Brown 2024-06-12 14:57:27 +00:00
parent 7eb887ca51
commit de57002c6f
1 changed files with 21 additions and 5 deletions
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26
src/core/operations/AffineCipherDecode.mjs
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@ -35,6 +35,11 @@ class AffineCipherDecode extends Operation {
"name": "b",
"type": "number",
"value": 0
},
{
"name": "Use modular inverse values",
"type": "boolean",
"value": false
}
];
}
@ -48,7 +53,7 @@ class AffineCipherDecode extends Operation {
*/
run(input, args) {
const alphabet = "abcdefghijklmnopqrstuvwxyz",
[a, b] = args,
[a, b, useInv] = args,
aModInv = Utils.modInv(a, 26); // Calculates modular inverse of a
let output = "";
@ -62,11 +67,22 @@ class AffineCipherDecode extends Operation {
for (let i = 0; i < input.length; i++) {
if (alphabet.indexOf(input[i]) >= 0) {
// Uses the affine decode function (y-b * A') % m = x (where m is length of the alphabet and A' is modular inverse)
output += alphabet[Utils.mod((alphabet.indexOf(input[i]) - b) * aModInv, 26)];
if (useInv) {
// Uses the affine decode function (y+b)*a % m, where m is the length
// of the alphabet and a,b are modular inverses of the original a,b
output += alphabet[Utils.mod((alphabet.indexOf(input[i]) + b) * a, 26)];
} else {
// Uses the affine decode function (y-b * A') % m = x (where m is length of the alphabet and A' is modular inverse)
output += alphabet[Utils.mod((alphabet.indexOf(input[i]) - b) * aModInv, 26)];
}
} else if (alphabet.indexOf(input[i].toLowerCase()) >= 0) {
// Same as above, accounting for uppercase
output += alphabet[Utils.mod((alphabet.indexOf(input[i].toLowerCase()) - b) * aModInv, 26)].toUpperCase();
if (useInv) {
// Same as above, accounting for uppercase
output += alphabet[Utils.mod((alphabet.indexOf(input[i].toLowerCase()) + b) * a, 26)].toUpperCase();
} else {
// Same as above, accounting for uppercase
output += alphabet[Utils.mod((alphabet.indexOf(input[i].toLowerCase()) - b) * aModInv, 26)].toUpperCase();
}
} else {
// Non-alphabetic characters
output += input[i];